dccp: Query supported CCIDs

This provides a data structure to record which CCIDs are locally supported
and three accessor functions:
 - a test function for internal use which is used to validate CCID requests
   made by the user;
 - a copy function so that the list can be used for feature-negotiation;   
 - documented getsockopt() support so that the user can query capabilities.

The data structure is a table which is filled in at compile-time with the
list of available CCIDs (which in turn depends on the Kconfig choices).

Using the copy function for cloning the list of supported CCIDs is useful for
feature negotiation, since the negotiation is now with the full list of available
CCIDs (e.g. {2, 3}) instead of the default value {2}. This means negotiation 
will not fail if the peer requests to use CCID3 instead of CCID2. 

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz>

1 files changed, 48 insertions, 0 deletions

diff --git a/net/dccp/ccid.c b/net/dccp/ccid.c
index 4809753d12ae..f72ca83df552 100644
--- a/net/dccp/ccid.c
+++ b/net/dccp/ccid.c
@@ -13,6 +13,13 @@
 
 #include "ccid.h"
 
+static u8 builtin_ccids[] = {
+        DCCPC_CCID2,            /* CCID2 is supported by default */
+#if defined(CONFIG_IP_DCCP_CCID3) || defined(CONFIG_IP_DCCP_CCID3_MODULE)
+        DCCPC_CCID3,
+#endif
+};
+
 static struct ccid_operations *ccids[CCID_MAX];
 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
 static atomic_t ccids_lockct = ATOMIC_INIT(0);
@@ -86,6 +93,47 @@ static void ccid_kmem_cache_destroy(struct kmem_cache *slab)
         }
 }
 
+/* check that up to @array_len members in @ccid_array are supported */
+bool ccid_support_check(u8 const *ccid_array, u8 array_len)
+{
+        u8 i, j, found;
+
+        for (i = 0, found = 0; i < array_len; i++, found = 0) {
+                for (j = 0; !found && j < ARRAY_SIZE(builtin_ccids); j++)
+                        found = (ccid_array[i] == builtin_ccids[j]);
+                if (!found)
+                        return false;
+        }
+        return true;
+}
+
+/**
+ * ccid_get_builtin_ccids  -  Provide copy of `builtin' CCID array
+ * @ccid_array: pointer to copy into
+ * @array_len: value to return length into
+ * This function allocates memory - caller must see that it is freed after use.
+ */
+int ccid_get_builtin_ccids(u8 **ccid_array, u8 *array_len)
+{
+        *ccid_array = kmemdup(builtin_ccids, sizeof(builtin_ccids), gfp_any());
+        if (*ccid_array == NULL)
+                return -ENOBUFS;
+        *array_len = ARRAY_SIZE(builtin_ccids);
+        return 0;
+}
+
+int ccid_getsockopt_builtin_ccids(struct sock *sk, int len,
+                                    char __user *optval, int __user *optlen)
+{
+        if (len < sizeof(builtin_ccids))
+                return -EINVAL;
+
+        if (put_user(sizeof(builtin_ccids), optlen) ||
+            copy_to_user(optval, builtin_ccids, sizeof(builtin_ccids)))
+                return -EFAULT;
+        return 0;
+}
+
 int ccid_register(struct ccid_operations *ccid_ops)
 {
         int err = -ENOBUFS;